Unsaturated fatty acids are also called, highly unsaturated fatty acids or poly unsaturated fatty acids (PAUF). Particularly the unsaturated fatty acids useful to a human body are an omega-3 (ω-3) fatty acid and an omega-6 (ω-6) fatty acid, and the omega-3 fatty acid has a double bond at the third carbon, and the omega-6 fatty acid does not have a double bond before the sixth carbon. Representative examples of the omega-3 unsaturated fatty acid include docosahexaenoic acid (DHA) having a carbon chain length of 22 with 6 double bonds starting from the third carbon from the methyl end, and represented by “22:6n-3”, eicosapentaenoic acid (EPA) represented by “20:5n-3”, docosapentaenoic acid (DPA) represented by “22:5n-3”, α-linolenic acid represented by “16:3n-3”, and the like, which are known as very useful kinds of an omega-3 unsaturated fatty acid, and the omega-6 unsaturated fatty acid includes arachidonic acid (ARA) represented by “20:4n-6”, and the like.
The unsaturated fatty acids as the above play a very important role in a body: it is known that the omega-3 unsaturated fatty acid prevents arteriosclerosis and a coronary heart disease, mitigates an inflammatory condition, and delays growth of tumor cells; and the omega-6 unsaturated fatty acid functions as a structural lipid in a human body, and also as a precursor of numerous factors in inflammation such as prostaglandin, leukotriene and oxylipin. Particularly, docosahexaenoic acid (DHA) is known as an essential fatty acid in brain, an ocular tissue, and a nervous system, particularly having an important function in development of eyesight and psychomotor ability of an infant, and abundant in retina, semen and a brain tissue of a human being and an animal. Particularly, DHA is an essential fatty acid constituting 60% of brain fat. The docosahexaenoic acid is known as being important for healthy development of brain, eyes, and a nervous system of an infant, together with arachidonic acid (ARA), and has been reported to be effective in prevention and treatment of numerous diseases ranging from cancer to arthritis, cardiovascular diseases, and mental disorders, and recently, its various anti-aging functions such as suppression of macular degeneration of presbyopia have been newly discovered.
Since such omega-3 or omega-6 unsaturated fatty acid has an important function in a human body, it is recommended by the World Health Organization (WHO) that omega-3 unsaturated fatty acid should account for 1-2% of daily energy intake, which corresponds to about 2.2 to 4.4 g based on 2000 kcal of meal, and it is recommended by certified organizations in each country to consistently take 1 g or more of DHA a day. Therefore, DHA has been commercialized as various products such as health functional food, and also has high potential as pharmaceutical raw materials, and thus, it can be said that the commercial value of DHA is very high.
However, since such omega-3 or omega-6 unsaturated fatty acid is not naturally synthesized in a human body, there is a difficulty that those fatty acids should be ingested mainly through food.
Previously, the omega-3 or omega-6 unsaturated fatty acid has been ingested through vegetable oil, marine animal oil, fish oil, oilseeds, and the like, and representatively has been supplied by direct ingestion of fish oil contained in fish. The fish containing a high content of EPA and DHA is mackerel, herring, salmon, and the like, and some fish such as cod and haddock reserves most of fat in liver. Nevertheless, the best source is cold water fish such as tuna, mackerel, sardines, herring and trout. However, in order to efficiently receive DHA from fish oil, it is preferred to eat raw or boiled fish, and moreover, it is necessary to eat peel in rear gill of dorsal circumference and along abdomen, because most of oil is accumulated in those parts. However, since fish oil decays rapidly, and decayed fish smells fishy odor, it has a disadvantage of not whetting appetite very much, and has a serious pollution problem by heavy metals and organic chemical materials of the fish oil. Particularly, in order to obtain fish oil in a sufficient amount to a human body, a large amount of fish is needed, and thus, practically, it is very difficult to meet such requirements economically on an industrial scale.
In order to solve these problems, research of a method of preparing omega-3 unsaturated fatty acid including docosahexaenoic acid by culturing various microorganisms including algae has proceeded. Particularly, interest in fine-heterotrophic bacteria called Thraustochytrid has been increased, which are a non-photosynthetic heterotrophic microorganism group classified into Stramenophila kingdom together with oomycetes and labyrinthulids. Thraustochytrid includes Schizochytrium, Aurantiochytrium and Thraustochytrium genera, and the species constituting those genera have been spotlighted as a potential omega-3 source for industrial use, due to their high lipid content and high level of DHA. Thraustochytrid is a saprobe, or in some cases, a trivial name of fine heterotrophic bacteria supplied as a saprophyte. Thraustochytrid has wide geographical distribution together with strain separated from the Antarctic Continent, the North Sea, India, Japan and Australia. It is rarely found in living plants, and appears to be inhibited by plant antimicrobials. The species constituting this group are abundant sometimes in a dead autochthonous organism of indigenousness macro-algae, aquatic Mangrove leaves and the like, as well as allochthonous plant materials. They are present usually in water column including coast and deep sea, and in a deposit.
A preparation method of omega-3 unsaturated fatty acid by Thraustochytrium and Schizochytrium genera microorganisms which are a kind of marine microalgae has been already known since the late 1960s (Ellenbogen B. B. et al., Comp. Biochem. Physiol., 29:805-811, 1969), and Martek which is estimated to have the most advanced technology has developed a method of producing omega-3 unsaturated fatty acid using Schizochytrium sp. ATCC 20888 and Schizochytrium sp. ATCC 20889 which are microorganisms of a Schizochytrium genus (U.S. Pat. Nos. 5,130,242B and 5,340,742B). In addition, Suntory has reported Schizochytrium limacinum SR21 as a microorganism having excellent docosahexaenoic acid productivity (Japanese Patent Laid-Open Publication No. 1997-000284A, and U.S. Pat. No. 6,582,941B).
There are still a number of researches in progress, however, a demand for new microalgae having high productivity and process efficiency, and particularly an ability to environmentally friendly mass-produce bio-oil is urgent.
Accordingly, the present inventors exerted all efforts to develop microalgae having high unsaturated fatty acid producibility, while having high efficiency of a culture process, and as a result, confirmed that microalgae of a Thraustochytrid were separated from a coastal wetland or a hot springs area wetland having a high temperature and rich in organic materials, and in case of using the microalgae, omega-3 and additionally omega-6 unsaturated fatty acids may be efficiently and economically produced, and thus, completed the present invention.